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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="container.non_standard_containers"></a><a class="link" href="non_standard_containers.html" title="Non-standard containers">Non-standard containers</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="non_standard_containers.html#container.non_standard_containers.stable_vector"><span class="emphasis"><em>stable_vector</em></span></a></span></dt>
<dt><span class="section"><a href="non_standard_containers.html#container.non_standard_containers.flat_xxx"><span class="emphasis"><em>flat_(multi)map/set</em></span>
      associative containers</a></span></dt>
<dt><span class="section"><a href="non_standard_containers.html#container.non_standard_containers.devector"><span class="emphasis"><em>devector</em></span></a></span></dt>
<dt><span class="section"><a href="non_standard_containers.html#container.non_standard_containers.slist"><span class="emphasis"><em>slist</em></span></a></span></dt>
<dt><span class="section"><a href="non_standard_containers.html#container.non_standard_containers.static_vector"><span class="emphasis"><em>static_vector</em></span></a></span></dt>
<dt><span class="section"><a href="non_standard_containers.html#container.non_standard_containers.small_vector"><span class="emphasis"><em>small_vector</em></span></a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.non_standard_containers.stable_vector"></a><a class="link" href="non_standard_containers.html#container.non_standard_containers.stable_vector" title="stable_vector"><span class="emphasis"><em>stable_vector</em></span></a>
</h3></div></div></div>
<p>
        This useful, fully STL-compliant stable container <a href="http://bannalia.blogspot.com/2008/09/introducing-stablevector.html" target="_top">designed
        by Joaquín M. López Muñoz</a> is an hybrid between <code class="computeroutput"><span class="identifier">vector</span></code> and <code class="computeroutput"><span class="identifier">list</span></code>,
        providing most of the features of <code class="computeroutput"><span class="identifier">vector</span></code>
        except <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#69" target="_top">element
        contiguity</a>.
      </p>
<p>
        Extremely convenient as they are, <code class="computeroutput"><span class="identifier">vector</span></code>s
        have a limitation that many novice C++ programmers frequently stumble upon:
        iterators and references to an element of an <code class="computeroutput"><span class="identifier">vector</span></code>
        are invalidated when a preceding element is erased or when the vector expands
        and needs to migrate its internal storage to a wider memory region (i.e.
        when the required size exceeds the vector's capacity). We say then that
        <code class="computeroutput"><span class="identifier">vector</span></code>s are unstable: by
        contrast, stable containers are those for which references and iterators
        to a given element remain valid as long as the element is not erased: examples
        of stable containers within the C++ standard library are <code class="computeroutput"><span class="identifier">list</span></code>
        and the standard associative containers (<code class="computeroutput"><span class="identifier">set</span></code>,
        <code class="computeroutput"><span class="identifier">map</span></code>, etc.).
      </p>
<p>
        Sometimes stability is too precious a feature to live without, but one particular
        property of <code class="computeroutput"><span class="identifier">vector</span></code>s, element
        contiguity, makes it impossible to add stability to this container. So, provided
        we sacrifice element contiguity, how much can a stable design approach the
        behavior of <code class="computeroutput"><span class="identifier">vector</span></code> (random
        access iterators, amortized constant time end insertion/deletion, minimal
        memory overhead, etc.)? The following image describes the layout of a possible
        data structure upon which to base the design of a stable vector:
      </p>
<p>
        <span class="inlinemediaobject"><img src="../../../libs/container/doc/images/stable_vector.png" align="middle" width="50%" alt="stable_vector"></span>
      </p>
<p>
        Each element is stored in its own separate node. All the nodes are referenced
        from a contiguous array of pointers, but also every node contains an "up"
        pointer referring back to the associated array cell. This up pointer is the
        key element to implementing stability and random accessibility:
      </p>
<p>
        Iterators point to the nodes rather than to the pointer array. This ensures
        stability, as it is only the pointer array that needs to be shifted or relocated
        upon insertion or deletion. Random access operations can be implemented by
        using the pointer array as a convenient intermediate zone. For instance,
        if the iterator it holds a node pointer <code class="computeroutput"><span class="identifier">it</span><span class="special">.</span><span class="identifier">p</span></code> and
        we want to advance it by n positions, we simply do:
      </p>
<pre class="programlisting"><span class="identifier">it</span><span class="special">.</span><span class="identifier">p</span> <span class="special">=</span> <span class="special">*(</span><span class="identifier">it</span><span class="special">.</span><span class="identifier">p</span><span class="special">-&gt;</span><span class="identifier">up</span><span class="special">+</span><span class="identifier">n</span><span class="special">);</span>
</pre>
<p>
        That is, we go "up" to the pointer array, add n there and then
        go "down" to the resulting node.
      </p>
<p>
        <span class="bold"><strong>General properties</strong></span>. <code class="computeroutput"><span class="identifier">stable_vector</span></code>
        satisfies all the requirements of a container, a reversible container and
        a sequence and provides all the optional operations present in vector. Like
        vector, iterators are random access. <code class="computeroutput"><span class="identifier">stable_vector</span></code>
        does not provide element contiguity; in exchange for this absence, the container
        is stable, i.e. references and iterators to an element of a <code class="computeroutput"><span class="identifier">stable_vector</span></code> remain valid as long as the
        element is not erased, and an iterator that has been assigned the return
        value of end() always remain valid until the destruction of the associated
        <code class="computeroutput"><span class="identifier">stable_vector</span></code>.
      </p>
<p>
        <span class="bold"><strong>Operation complexity</strong></span>. The big-O complexities
        of <code class="computeroutput"><span class="identifier">stable_vector</span></code> operations
        match exactly those of vector. In general, insertion/deletion is constant
        time at the end of the sequence and linear elsewhere. Unlike vector, <code class="computeroutput"><span class="identifier">stable_vector</span></code> does not internally perform
        any value_type destruction, copy/move construction/assignment operations
        other than those exactly corresponding to the insertion of new elements or
        deletion of stored elements, which can sometimes compensate in terms of performance
        for the extra burden of doing more pointer manipulation and an additional
        allocation per element.
      </p>
<p>
        <span class="bold"><strong>Exception safety</strong></span>. (according to <a href="http://www.boost.org/community/exception_safety.html" target="_top">Abrahams'
        terminology</a>) As <code class="computeroutput"><span class="identifier">stable_vector</span></code>
        does not internally copy/move elements around, some operations provide stronger
        exception safety guarantees than in vector:
      </p>
<div class="table">
<a name="container.non_standard_containers.stable_vector.stable_vector_req"></a><p class="title"><b>Table 9.1. Exception safety</b></p>
<div class="table-contents"><table class="table" summary="Exception safety">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  operation
                </p>
              </th>
<th>
                <p>
                  exception safety for <code class="computeroutput"><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
                </p>
              </th>
<th>
                <p>
                  exception safety for <code class="computeroutput"><span class="identifier">stable_vector</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  insert
                </p>
              </td>
<td>
                <p>
                  strong unless copy/move construction/assignment of <code class="computeroutput"><span class="identifier">T</span></code> throw (basic)
                </p>
              </td>
<td>
                <p>
                  strong
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  erase
                </p>
              </td>
<td>
                <p>
                  no-throw unless copy/move construction/assignment of <code class="computeroutput"><span class="identifier">T</span></code> throw (basic)
                </p>
              </td>
<td>
                <p>
                  no-throw
                </p>
              </td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><p>
        <span class="bold"><strong>Memory overhead</strong></span>. The C++ standard does not
        specify requirements on memory consumption, but virtually any implementation
        of <code class="computeroutput"><span class="identifier">vector</span></code> has the same behavior
        with respect to memory usage: the memory allocated by a <code class="computeroutput"><span class="identifier">vector</span></code>
        v with n elements of type T is
      </p>
<p>
        m<sub>v</sub> = c∙e,
      </p>
<p>
        where c is <code class="computeroutput"><span class="identifier">v</span><span class="special">.</span><span class="identifier">capacity</span><span class="special">()</span></code>
        and e is <code class="computeroutput"><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">T</span><span class="special">)</span></code>. c can
        be as low as n if the user has explicitly reserved the exact capacity required;
        otherwise, the average value c for a growing <code class="computeroutput"><span class="identifier">vector</span></code>
        oscillates between 1.25∙n and 1.5∙n for typical resizing policies.
        For <code class="computeroutput"><span class="identifier">stable_vector</span></code>, the memory
        usage is
      </p>
<p>
        m<sub>sv</sub> = (c + 1)p + (n + 1)(e + p),
      </p>
<p>
        where p is the size of a pointer. We have c + 1 and n + 1 rather than c and
        n because a dummy node is needed at the end of the sequence. If we call f
        the capacity to size ratio c/n and assume that n is large enough, we have
        that
      </p>
<p>
        m<sub>sv</sub>/m<sub>v</sub> ≃ (fp + e + p)/fe.
      </p>
<p>
        So, <code class="computeroutput"><span class="identifier">stable_vector</span></code> uses less
        memory than <code class="computeroutput"><span class="identifier">vector</span></code> only when
        e &gt; p and the capacity to size ratio exceeds a given threshold:
      </p>
<p>
        m<sub>sv</sub> &lt; m<sub>v</sub> &lt;-&gt; f &gt; (e + p)/(e - p). (provided e &gt; p)
      </p>
<p>
        This threshold approaches typical values of f below 1.5 when e &gt; 5p; in
        a 32-bit architecture, when e &gt; 20 bytes.
      </p>
<p>
        <span class="bold"><strong>Summary</strong></span>. <code class="computeroutput"><span class="identifier">stable_vector</span></code>
        is a drop-in replacement for <code class="computeroutput"><span class="identifier">vector</span></code>
        providing stability of references and iterators, in exchange for missing
        element contiguity and also some performance and memory overhead. When the
        element objects are expensive to move around, the performance overhead can
        turn into a net performance gain for <code class="computeroutput"><span class="identifier">stable_vector</span></code>
        if many middle insertions or deletions are performed or if resizing is very
        frequent. Similarly, if the elements are large there are situations when
        the memory used by <code class="computeroutput"><span class="identifier">stable_vector</span></code>
        can actually be less than required by vector.
      </p>
<p>
        <span class="emphasis"><em>Note: Text and explanations taken from <a href="http://bannalia.blogspot.com/2008/09/introducing-stablevector.html" target="_top">Joaquín's
        blog</a></em></span>
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.non_standard_containers.flat_xxx"></a><a class="link" href="non_standard_containers.html#container.non_standard_containers.flat_xxx" title="flat_(multi)map/set associative containers"><span class="emphasis"><em>flat_(multi)map/set</em></span>
      associative containers</a>
</h3></div></div></div>
<p>
        Using sorted vectors instead of tree-based associative containers is a well-known
        technique in C++ world. Matt Austern's classic article <a href="http://lafstern.org/matt/col1.pdf" target="_top">Why
        You Shouldn't Use set, and What You Should Use Instead</a> (C++ Report
        12:4, April 2000) was enlightening:
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>Red-black trees aren't the only way to organize data that
        permits lookup in logarithmic time. One of the basic algorithms of computer
        science is binary search, which works by successively dividing a range in
        half. Binary search is log N and it doesn't require any fancy data structures,
        just a sorted collection of elements. (...) You can use whatever data structure
        is convenient, so long as it provides STL iterator; usually it's easiest
        to use a C array, or a vector.</em></span></span>”</span>
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>Both std::lower_bound and set::find take time proportional
        to log N, but the constants of proportionality are very different. Using
        g++ (...) it takes X seconds to perform a million lookups in a sorted vector&lt;double&gt;
        of a million elements, and almost twice as long (...) using a set. Moreover,
        the set uses almost three times as much memory (48 million bytes) as the
        vector (16.8 million).</em></span></span>”</span>
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>Using a sorted vector instead of a set gives you faster
        lookup and much faster iteration, but at the cost of slower insertion. Insertion
        into a set, using set::insert, is proportional to log N, but insertion into
        a sorted vector, (...) , is proportional to N. Whenever you insert something
        into a vector, vector::insert has to make room by shifting all of the elements
        that follow it. On average, if you're equally likely to insert a new element
        anywhere, you'll be shifting N/2 elements.</em></span></span>”</span>
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>It may sometimes be convenient to bundle all of this together
        into a small container adaptor. This class does not satisfy the requirements
        of a Standard Associative Container, since the complexity of insert is O(N)
        rather than O(log N), but otherwise it is almost a drop-in replacement for
        set.</em></span></span>”</span>
      </p>
<p>
        Following Matt Austern's indications, Andrei Alexandrescu's <a href="http://www.bestwebbuys.com/Modern-C-Design-Generic-Programming-and-Design-Patterns-Applied-ISBN-9780201704310?isrc=-rd" target="_top">Modern
        C++ Design</a> showed <code class="computeroutput"><span class="identifier">AssocVector</span></code>,
        a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code> drop-in replacement designed in his
        <a href="http://loki-lib.sourceforge.net/" target="_top">Loki</a> library:
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>It seems as if we're better off with a sorted vector. The
        disadvantages of a sorted vector are linear-time insertions and linear-time
        deletions (...). In exchange, a vector offers about twice the lookup speed
        and a much smaller working set (...). Loki saves the trouble of maintaining
        a sorted vector by hand by defining an AssocVector class template. AssocVector
        is a drop-in replacement for std::map (it supports the same set of member
        functions), implemented on top of std::vector. AssocVector differs from a
        map in the behavior of its erase functions (AssocVector::erase invalidates
        all iterators into the object) and in the complexity guarantees of insert
        and erase (linear as opposed to constant). </em></span></span>”</span>
      </p>
<p>
        <span class="bold"><strong>Boost.Container</strong></span> <code class="computeroutput"><span class="identifier">flat_</span><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">map</span><span class="special">/</span><span class="identifier">set</span></code> containers are ordered, vector-like
        container based, associative containers following Austern's and Alexandrescu's
        guidelines. These ordered vector containers have also benefited with the
        addition of <code class="computeroutput"><span class="identifier">move</span> <span class="identifier">semantics</span></code>
        to C++11, speeding up insertion and erasure times considerably. Flat associative
        containers have the following attributes:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            Faster lookup than standard associative containers
          </li>
<li class="listitem">
            Much faster iteration than standard associative containers. Random-access
            iterators instead of bidirectional iterators.
          </li>
<li class="listitem">
            Less memory consumption for small objects (and for big objects if <code class="computeroutput"><span class="identifier">shrink_to_fit</span></code> is used)
          </li>
<li class="listitem">
            Improved cache performance (data is stored in contiguous memory)
          </li>
<li class="listitem">
            Non-stable iterators (iterators are invalidated when inserting and erasing
            elements)
          </li>
<li class="listitem">
            Non-copyable and non-movable values types can't be stored
          </li>
<li class="listitem">
            Weaker exception safety than standard associative containers (copy/move
            constructors can throw when shifting values in erasures and insertions)
          </li>
<li class="listitem">
            Slower insertion and erasure than standard associative containers (specially
            for non-movable types)
          </li>
</ul></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.non_standard_containers.devector"></a><a class="link" href="non_standard_containers.html#container.non_standard_containers.devector" title="devector"><span class="emphasis"><em>devector</em></span></a>
</h3></div></div></div>
<p>
        <code class="computeroutput"><span class="identifier">devector</span></code> is a hybrid of the
        standard vector and deque containers originally written by Thaler Benedek.
        It offers cheap (amortized constant time) insertion at both the front and
        back ends, while also providing the regular features of <code class="computeroutput"><span class="identifier">vector</span></code>,
        in particular the contiguous underlying memory.
      </p>
<p>
        Unlike <code class="computeroutput"><span class="identifier">vector</span></code>, devector can
        have free capacity both before and after the elements. This enables efficient
        implementation of methods that modify the devector at the front. In general,
        <code class="computeroutput"><span class="identifier">devector</span></code>'s available methods
        are a superset of those of <code class="computeroutput"><span class="identifier">vector</span></code>
        with identical behaviour, barring a couple of iterator invalidation guarantees
        that differ.
      </p>
<p>
        The overhead for devector is one extra <code class="computeroutput"><span class="identifier">size_t</span></code>
        per container: Usually sizeof(devector) == 4*sizeof(T*).
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.non_standard_containers.slist"></a><a class="link" href="non_standard_containers.html#container.non_standard_containers.slist" title="slist"><span class="emphasis"><em>slist</em></span></a>
</h3></div></div></div>
<p>
        When the standard template library was designed, it contained a singly linked
        list called <code class="computeroutput"><span class="identifier">slist</span></code>. Unfortunately,
        this container was not standardized and remained as an extension for many
        standard library implementations until C++11 introduced <code class="computeroutput"><span class="identifier">forward_list</span></code>,
        which is a bit different from the the original SGI <code class="computeroutput"><span class="identifier">slist</span></code>.
        According to <a href="http://www.sgi.com/tech/stl/Slist.html" target="_top">SGI STL
        documentation</a>:
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>An <code class="computeroutput"><span class="identifier">slist</span></code>
        is a singly linked list: a list where each element is linked to the next
        element, but not to the previous element. That is, it is a Sequence that
        supports forward but not backward traversal, and (amortized) constant time
        insertion and removal of elements. Slists, like lists, have the important
        property that insertion and splicing do not invalidate iterators to list
        elements, and that even removal invalidates only the iterators that point
        to the elements that are removed. The ordering of iterators may be changed
        (that is, slist&lt;T&gt;::iterator might have a different predecessor or
        successor after a list operation than it did before), but the iterators themselves
        will not be invalidated or made to point to different elements unless that
        invalidation or mutation is explicit.</em></span></span>”</span>
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>The main difference between <code class="computeroutput"><span class="identifier">slist</span></code>
        and list is that list's iterators are bidirectional iterators, while slist's
        iterators are forward iterators. This means that <code class="computeroutput"><span class="identifier">slist</span></code>
        is less versatile than list; frequently, however, bidirectional iterators
        are unnecessary. You should usually use <code class="computeroutput"><span class="identifier">slist</span></code>
        unless you actually need the extra functionality of list, because singly
        linked lists are smaller and faster than double linked lists.</em></span></span>”</span>
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>Important performance note: like every other Sequence,
        <code class="computeroutput"><span class="identifier">slist</span></code> defines the member
        functions insert and erase. Using these member functions carelessly, however,
        can result in disastrously slow programs. The problem is that insert's first
        argument is an iterator pos, and that it inserts the new element(s) before
        pos. This means that insert must find the iterator just before pos; this
        is a constant-time operation for list, since list has bidirectional iterators,
        but for <code class="computeroutput"><span class="identifier">slist</span></code> it must find
        that iterator by traversing the list from the beginning up to pos. In other
        words: insert and erase are slow operations anywhere but near the beginning
        of the slist.</em></span></span>”</span>
      </p>
<p>
        <span class="quote">“<span class="quote"><span class="emphasis"><em>Slist provides the member functions insert_after and erase_after,
        which are constant time operations: you should always use insert_after and
        erase_after whenever possible. If you find that insert_after and erase_after
        aren't adequate for your needs, and that you often need to use insert and
        erase in the middle of the list, then you should probably use list instead
        of slist.</em></span></span>”</span>
      </p>
<p>
        <span class="bold"><strong>Boost.Container</strong></span> updates the classic <code class="computeroutput"><span class="identifier">slist</span></code> container with C++11 features like
        move semantics and placement insertion and implements it a bit differently
        than the standard C++ <code class="computeroutput"><span class="identifier">forward_list</span></code>.
        <code class="computeroutput"><span class="identifier">forward_list</span></code> has no <code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>
        method, so it's been designed to allow (or in practice, encourage) implementations
        without tracking list size with every insertion/erasure, allowing constant-time
        <code class="computeroutput"><span class="identifier">splice_after</span><span class="special">(</span><span class="identifier">iterator</span><span class="special">,</span> <span class="identifier">forward_list</span> <span class="special">&amp;,</span>
        <span class="identifier">iterator</span><span class="special">,</span>
        <span class="identifier">iterator</span><span class="special">)</span></code>-based
        list merging. On the other hand <code class="computeroutput"><span class="identifier">slist</span></code>
        offers constant-time <code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code> for those that don't care about linear-time
        <code class="computeroutput"><span class="identifier">splice_after</span><span class="special">(</span><span class="identifier">iterator</span><span class="special">,</span> <span class="identifier">slist</span> <span class="special">&amp;,</span>
        <span class="identifier">iterator</span><span class="special">,</span>
        <span class="identifier">iterator</span><span class="special">)</span></code>
        <code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>
        and offers an additional <code class="computeroutput"><span class="identifier">splice_after</span><span class="special">(</span><span class="identifier">iterator</span><span class="special">,</span> <span class="identifier">slist</span> <span class="special">&amp;,</span> <span class="identifier">iterator</span><span class="special">,</span> <span class="identifier">iterator</span><span class="special">,</span> <span class="identifier">size_type</span><span class="special">)</span></code> method that can speed up <code class="computeroutput"><span class="identifier">slist</span></code>
        merging when the programmer already knows the size. <code class="computeroutput"><span class="identifier">slist</span></code>
        and <code class="computeroutput"><span class="identifier">forward_list</span></code> are therefore
        complementary.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.non_standard_containers.static_vector"></a><a class="link" href="non_standard_containers.html#container.non_standard_containers.static_vector" title="static_vector"><span class="emphasis"><em>static_vector</em></span></a>
</h3></div></div></div>
<p>
        <code class="computeroutput"><span class="identifier">static_vector</span></code> is an hybrid
        between <code class="computeroutput"><span class="identifier">vector</span></code> and <code class="computeroutput"><span class="identifier">array</span></code>: like <code class="computeroutput"><span class="identifier">vector</span></code>,
        it's a sequence container with contiguous storage that can change in size,
        along with the static allocation, low overhead, and fixed capacity of <code class="computeroutput"><span class="identifier">array</span></code>. <code class="computeroutput"><span class="identifier">static_vector</span></code>
        is based on Adam Wulkiewicz and Andrew Hundt's high-performance <a href="https://svn.boost.org/svn/boost/sandbox/varray/doc/html/index.html" target="_top">varray</a>
        class.
      </p>
<p>
        The number of elements in a <code class="computeroutput"><span class="identifier">static_vector</span></code>
        may vary dynamically up to a fixed capacity because elements are stored within
        the object itself similarly to an array. However, objects are initialized
        as they are inserted into <code class="computeroutput"><span class="identifier">static_vector</span></code>
        unlike C arrays or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">array</span></code> which must construct all elements
        on instantiation. The behavior of <code class="computeroutput"><span class="identifier">static_vector</span></code>
        enables the use of statically allocated elements in cases with complex object
        lifetime requirements that would otherwise not be trivially possible. Some
        other properties:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            Random access to elements
          </li>
<li class="listitem">
            Constant time insertion and removal of elements at the end
          </li>
<li class="listitem">
            Linear time insertion and removal of elements at the beginning or in
            the middle.
          </li>
</ul></div>
<p>
        <code class="computeroutput"><span class="identifier">static_vector</span></code> is well suited
        for use in a buffer, the internal implementation of other classes, or use
        cases where there is a fixed limit to the number of elements that must be
        stored. Embedded and realtime applications where allocation either may not
        be available or acceptable are a particular case where <code class="computeroutput"><span class="identifier">static_vector</span></code>
        can be beneficial.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.non_standard_containers.small_vector"></a><a class="link" href="non_standard_containers.html#container.non_standard_containers.small_vector" title="small_vector"><span class="emphasis"><em>small_vector</em></span></a>
</h3></div></div></div>
<p>
        <code class="computeroutput"><span class="identifier">small_vector</span></code> is a vector-like
        container optimized for the case when it contains few elements. It contains
        some preallocated elements in-place, which allows it to avoid the use of
        dynamic storage allocation when the actual number of elements is below that
        preallocated threshold. <code class="computeroutput"><span class="identifier">small_vector</span></code>
        is inspired by <a href="http://llvm.org/docs/ProgrammersManual.html#llvm-adt-smallvector-h" target="_top">LLVM's
        <code class="computeroutput"><span class="identifier">SmallVector</span></code></a> container.
        Unlike <code class="computeroutput"><span class="identifier">static_vector</span></code>, <code class="computeroutput"><span class="identifier">small_vector</span></code>'s capacity can grow beyond
        the initial preallocated capacity.
      </p>
<p>
        <code class="computeroutput"><span class="identifier">small_vector</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">&gt;</span></code> is convertible to <code class="computeroutput"><span class="identifier">small_vector_base</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span>
        <span class="identifier">Allocator</span><span class="special">&gt;</span></code>,
        a type that is independent from the preallocated element count, allowing
        client code that does not need to be templated on that N argument. <code class="computeroutput"><span class="identifier">small_vector</span></code> inherits all <code class="computeroutput"><span class="identifier">vector</span></code>'s member functions so it supports
        all standard features like emplacement, stateful allocators, etc.
      </p>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2009-2018 Ion Gaztanaga<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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